Powered lance assemblies have been used for decades to clean the tubes of heat exchanger bundle assemblies. Those familiar with industrial heat exchange equipment and chemical processing techniques recognize that a variety of tube bundle assemblies are mounted at various elevations and orientations in industrial and chemical plants, and that the elongate tubes in these heat exchanger bundles must be periodically cleaned to maintain proper processing efficiency. While such tube bundles have been cleaned for years with powered equipment, i.e., equipment using a powered force to drive the lance through a tube, it is not uncommon today for bundles to be cleaned manually, or to be cleaned with outdated equipment. In many instances, more complex and expensive cleaning equipment cannot be practically positioned for cleaning the tube bundle in place, and the tube bundle cannot be removed from the plant, cleaned, then reinstalled in a cost-effective manner. To clean industrial tube bundles on a cost-effective basis, the lance assembly ideally has a powered drive to pass the lance through the tube bundle, and the assembly uses a plurality of lance tubes, so that the equipment may be used for simultaneously cleaning multiple tubes of the tube bundle to reduce the overall time for cleaning the tube bundle.
Various techniques and concepts of thus been devised for cleaning tube bundles. U.S. Pat. No. 4,095,305 discloses tube bundle cleaning equipment including a frame for mounting a lance, track members, and a carriage. U.S. Pat. No. 4,085,653 discloses cleaning equipment which is essentially mounted on the end of a mobile machine, such as a truck. U.S. Pat. Nos. 5,002,120, 5,022,463, 5,067,558, and 5,129,455 are each directed to lance tube cleaning equipment having a spool assembly used to store a flexible water line, a lance assembly supplied with water from the spool assembly, and a positioned assembly for supporting the spool assembly and lance assembly so that the lance assembly can be raised to its proper elevation relative to the tube bundle to be cleaned. U.S. Pat. No. 4,856,545 discloses a multi-lance tube bundle cleaner which utilizes a linked drag chain for transporting water from the lower end of the lance housing to the powered lances in the upper end of the housing. U.S. Pat. No. 5,031,691 discloses a similar lance assembly which may be used to clean either horizontal or vertical tube bundle assemblies. A slidable plate is used to cover the elongate opening in the lance housing during reciprocal movement of the lances.
Prior art lance assemblies for cleaning tube bundles have a number of problems which have limited their efficiency and thus their utility. As discussed briefly above, one of the major problems concerns the size of lance assembly equipment itself, which in many cases is so massive that the equipment cannot be easily positioned for cleaning the tube bundle while the tube bundle remains in place in the plant, particularly in areas where access is restricted. Many prior art lance assemblies thus require that the tube bundle be removed from the plant, cleaned at a location exterior of the plant, then returned for installation in the plant. Even when the tube bundle is removed for cleaning, many prior art lance assemblies require that the tube bundle be elevated and blocked, or that the bundle remain raised off the floor by a crane, so that the lance assembly can practically clean the tube bundle. The pumping unit which supplies pressure to the lances is often mounted with the lance assembly, and these prior art lance assemblies effectively require that the lance assembly and the pumping unit each be positioned with respect to the tube bundle to be lanced, thereby again increasing the size and limiting the versatility of the lance assembly.
Another significant problem concerning prior art lance assemblies has to do with the significant pressure drop which undesirably occurs between the pumping unit and the discharge end of the lances, particularly when pumping pressure is high. Some prior art lance assemblies utilize a plurality of small diameter hoses extending to the lance manifold, which results in a significant pressure drop. Other lance assemblies coil the hoses supplying fluid to the lances in a reel assembly, thereby minimizing the pressure which can practically be supplied to the lances. In some prior art lance assemblies, the manifold distributing fluid to the plurality of lances is located a substantial distance upstream from the lances rather than being positioned adjacent the lances, and accordingly the pressure drop through the system is relatively high. This pressure drop significantly detracts from the efficiency of the lancing assembly to perform its cleaning function, and in many applications this pressure loss substantially increases the time for an operating crew to properly clean the tube bundle. Other prior lance assemblies provide for operator control of the lance speed relative to the tube bundle, but it is difficult to achieve the desired combination of speed and force to move the multi-lances through the tube bundle to perform their cleaning operation. As a consequence, the risk is high that a lance may become jammed and ruin one of the tubes within the bundle being cleaned, thus significantly increasing the overall repair costs.
Some lance assemblies are designed to be picked up vertically, e.g., by a crane, for positioning with respect to an elevated tube bundle for performing a horizontal lancing operation. In many cases, however, the lance assembly itself is so massive and heavy, and/or the crane hook-up attachment is so attached to the lance housing, that the task of positioning the lance assembly with respect to the tube bundle is both difficult and time consuming. Other prior art lancing assemblies which are elevated for use to clean a tube bundle effectively require that scaffolding be provided, so that the cleaning crew can effectively perform their cleaning operation. The cost of the scaffolding and erection time thus must be considered in determining the overall cost of the tube bundle cleaning operation.
The disadvantages of prior art are overcome by the present invention, and an improved tube bundle cleaning assembly and technique for cleaning bundles is hereinafter disclosed which, in a safe and reliable manner, will effectively reduce the cost associated with cleaning a tube bundle.